When I crank the engine, some time nothing happen, I either have to hold the key in that position for about 1-2 sec. then the engine will start or I have to turn key back and re-crank it. I have read this is one of the symptoms of faulty tumbler, is this right? The battery is about 2 years old, I only drive this car once a week. At first I thought was a weak battery/recharge, but after a 30 miles drive to work, it still happen sometime. It is a 90' /43000 miles. Any other thought?

Your problem sounds like an electrical failure. Check the obvious first, like loose or dirty battery terminal connections. Then I would check ground connections from the body to the trans. mounting bolts. This is under the drivers side of the car near the steering box. A tired starter is a definate possibiliy and next time it happens wiggle the shifter between Park and Neutral, if this has some effect then a neutral safety switch is the culprit.
The tumbler problem is related to the key not wanting to rotate in the dash. One last thought, the ignition switch could have a dead spot but that would be a unusual thing to happen to your model. Good luck!